This invention relates to a process wherein a fluid stream containing hydrogen sulfide is contacted with an aqueous solution containing a polyvalent metal chelate and the hydrogen sulfide in said steam is removed.
It is known from U.S Pat. No. 4,123,506 dated Oct. 31, 1978 and U.S. Pat. No. 4,202,864, dated May 13, 1980 that geothermal steam containing H.sub.2 S can be purified by contacting the steam with a metal compound that forms insoluble metallic sulfides.
It is also known from U.S. Pat. No. 4,196,183, dated Apr. 1, 1980 that geothermal steam containing H.sub.2 S can be purified by adding oxygen and passing it through an activated carbon bed.
Various processes for hydrogen sulfide control in geothermal steam are outlined in the U.S. Department of Energy Report #DOW/EV-0068 (March, 1980) by F. B. Stephens, et al.
U.S. Pat. No. 4,009,251, dated Feb. 22, 1977 discloses the removal of hydrogen sulfide from gaseous streams with metal chelates to form sulfur substantially without the formation of sulfur oxides.
In U.S. Pat. No. 4,414,817 dated Nov. 15, 1983, there is disclosed a process for the removal of hydrogen sulfide from geothermal steam. However, this process generates free sulfur or sulfur solids which must be removed. The instant process is superior in that the sulfur solids are minimized by being converted to soluble sulfur compounds.
In U.S. Pat. No. 4,451,442, dated May 29, 1984, there is disclosed a process for the removal of hydrogen sulfide from geothermal streams with minimum solid sulfer production. In this process, hydrogen sulfide is removed from fluid streams containing the same using a polyvalent metal chelate and an oxidizing agent. The oxidizing agent is preferably sulfur dioxide which can be generated by oxidizing a side stream of the hydrogen sulfide. However, in this process, the production of SO.sub.2 also forms CO.sub.2 which results in the formation of insoluble carbonates. These insoluble salts are troublesome and costly in geothermal power plants and other applications where solids free operation is necessary or desirable.
In U.S. Pat. No. 4,622,212, dated Nov. 11, 1986, there is described a hydrogen sulfide removal method using a chelating solution containing thiosulfate as a stabilizer.
In U.S. Pat. No. 3,446,595, dated May 27, 1969, there is described a gas purification process in which hydrogen sulfide is absorbed with bisulfite to form elemental sulfur and sulfite. This sulfite is regenerated to form bisulfite by contact with sulfur dioxide which in turn is formed by combustion of the elemental sulfur.
U.S. Pat. No. 3,859,414, dated Jan. 7, 1975, describes a process in which sulfite is reacted with hydrogen sulfide in a gas stream at thiosulfate forming conditions, e.g. a pH between 6 and 7, to form soluble sulfur compounds.
Other references which may be relevant to the instant disclosure include U.S. Pat. Nos. 4,629,608; 3,447,903; and 3,851,050.